Abstract. In tobacco (Nicotiana tabacum L.), long and short trichomes can be distinguished morphologically. The established function of long trichomes is to exude a sticky gum containing diterpenes, whereas that of short trichomes is not known. When tobacco seedlings were exposed to toxic levels of cadmium (Cd), growth was retarded, but trichome number was increased up to 2-fold in comparison with untreated samples. Observation by variable-pressure scanning electron microscopy (VP-SEM) indicated that large crystals of 150 μm in size were formed on head cells of both short and long trichomes. An energy-dispersive X-ray analysis system fitted with VP-SEM revealed the crystals to contain amounts of Cd and calcium (Ca) at much higher concentrations than in the head cells themselves. Transmission electron microscopy demonstrated crystal formation in amorphous osmiophilic deposits in vacuoles. When seedlings were treated with Cd in the presence of Ca, tolerance was increased in proportion to the increase in Ca concentration. These results indicate that tobacco plants actively exclude toxic Cd by forming and excreting Cd/Ca-containing crystals through the head cells of trichomes.

Detoxification of Cadmium in Tobacco Plants: Formation and Active Excretion of Crystals Containing Cadmium and Calcium Through Trichomes

Green infrastructure for air quality improvement in street canyons.

There are thousands of case studies documenting invasive species’ impacts and these have led to the development of over 30 hypotheses that describe how invasions occur and their impacts manifest. The proliferation of invasion hypotheses over the decades has spurred several efforts to identify conceptual overlap and increase clarity of impact mechanism in the field. What is still lacking, however, is a comprehensive accounting of the evidence base on invasive species impacts, especially in regard to the biological scales, temporal scales, and taxonomic groups that receive research. Identifying the ‘known unknowns’ of empirical invasion impact research serves a critical function in the effort to evaluate support for existing hypotheses and generate novel hypotheses. We built a taxonomically and geographically comprehensive database of over 1500 research articles that report measures of invasive species’ ecological impacts published over the past 18 years (1999–2016). We found that, field-wide, published measures of invasive species’ impacts are highly skewed toward those measured at the population or community-level with scarce information on impacts at other biological scales (e.g., physiology, behavior). We also show that existing impact evidence stems most often from one-off studies of single invasive species. Yet, even for species that receive consistent attention, impacts have rarely been documented across more than one biological scale, beyond very short time periods, or in several ecosystems. In order to predict and anticipate how impacts manifest in a variety of temporal and biological contexts, the evidence base informing existing invasion hypotheses must become more integrative both within and across publications.

https://link.springer.com/content/pdf/10.1007/s10530-020-02200-0.pdf

The ‘known unknowns’ of invasive species impact measurement

With increasing evidence that exposures to air pollution near large roadways increases risks of a number of adverse human health effects, identifying methods to reduce these exposures has become a public health priority. Roadside vegetation barriers have shown the potential to reduce near-road air pollution concentrations; however, the characteristics of these barriers needed to ensure pollution reductions are not well understood. Designing vegetation barriers to mitigate near-road air pollution requires a mechanistic understanding of how barrier configurations affect the transport of traffic-related air pollutants. We first evaluated the performance of the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) model with Large Eddy Simulation (LES) to capture the effects of vegetation barriers on near-road air quality, compared against field data. Next, CTAG with LES was employed to explore the effects of six conceptual roadside vegetation/solid barrier configurations on near-road size-resolved particle concentrations, governed by dispersion and deposition. Two potentially viable design options are revealed: a) a wide vegetation barrier with high Leaf Area Density (LAD), and b) vegetation-solid barrier combinations, i.e., planting trees next to a solid barrier. Both designs reduce downwind particle concentrations significantly. The findings presented in the study will assist urban planning and forestry organizations with evaluating different green infrastructure design options.

Supporting Information for "Roadside Vegetation Barrier Designs to Mitigate Near-Road Air Pollution Impacts"

Urban Heat Island (UHI) is a worldwide threat affecting building energy demand, public health, and energy security. Green wall deployment can simultaneously positively impact UHI and building energy demand depending on climate zones. According to the different climate zones worldwide, the present systematic literature review (SLR) investigates the direct effects of green wall installation on building energy use and UHI. 1325 articles were screened, and 51, corresponding to 647 case studies, were selected after removing those with methodological or statistical heterogeneity. The effects of green wall deployment have been explored according to cooling and heating season, weather conditions, daytime, nighttime, green wall typology, green wall orientation, and application scale. The performed analyses show that green walls: (1) can reduce heating and cooling building energy demand up to 16.5% and ∼51%, respectively, and mitigate UHI up to ∼5 °C in all the investigated climate zones; (2) can decrease to the greatest extent building energy needs when applied in low-density urban contexts where they can be installed on the entire building. Besides, when applied to a single façade, South orientation should be preferred in most climate zones to maximize building energy saving; (3) have the best UHI mitigating potential—up to 8 °C—in highly urbanized areas featured with narrow streets surrounded by high-rising buildings. Altogether, green walls are a fit-all solution to reduce building energy demand and mitigate UHI, providing healthier living conditions. However, further research is necessary to include quantifiable and unquantifiable effects omitted in the current study. • Green walls have been investigated in different climate zones. • The effect of green wall deployment on building energy use and UHI was explored. • Green wall deployment decreases building energy needs for space heating and cooling. • Green wall installation may reduce air temperature by up to 8 °C in street canyons. • Large-scale installation of green walls may fully mitigate UHI. 

Effect of green wall installation on urban heat island and building energy use: A climate-informed systematic literature review

In order to better design greening systems for effective particulate matter (PM) removal, it is important to understand the impact leaf traits have on PM deposition. There are however, inconsistenc...

/pdf/airborne-particulate-matter-accumulation-on-common-green-58gy6gw3fd.pdf

Airborne particulate matter accumulation on common green wall plants.

Green walls have previously demonstrated the capacity to reduce particulate matter (PM), noise pollution, and temperature conditions in manipulative experiments and computational models. There is, however, minimal evidence that green walls can influence ambient environmental conditions, especially taking into account the variable environmental conditions encountered in situ. The aim of this paper was to determine if green walls have a quantitative effect on ambient air quality in an urban environment. Ambient PM, noise, and temperature were recorded at 12 green wall and adjacent reference wall locations across a dense urban centre, over a 6-month period. The results indicated that PM levels and temperature did not significantly differ between the green wall and reference wall sites. Ambient noise at the green wall sites, however, was significantly lower than at the reference wall locations. It is suggested that mechanically assisted, or ‘active’ green wall systems may have a higher PM and temperature reduction capacity, and if so, they will be more valuable for installation in situ compared to standard passive systems, although this will require further research.

Can Green Walls Reduce Outdoor Ambient Particulate Matter, Noise Pollution and Temperature?

/pdf/landscape-variation-in-plant-leaf-flammability-is-driven-by-2lzjyfjgu7.pdf

Landscape variation in plant leaf flammability is driven by leaf traits responding to environmental gradients

Green wall plant tolerance to ambient urban air pollution

The planting of trees in streets and parks is critical for urban greening efforts that seek to improve climate-change resilience in cities around the world. Ecosystem services provided by urban trees range from mitigating urban heat island effects to enhancing human well-being and conserving native biodiversity. At the same time, such tree services trade off with disservices that include risk to human safety from falling branches and infrastructure damage from root growth. Here, we performed a survey of residents of a sub-tropical region in eastern Australia to determine community perceptions of the ecosystem services and disservices linked to urban tree plantings. Our aim was to better understand the diverse perceptions of the community, prior to on-the-ground implementation of urban greening, to help guide planting programs in streets and parklands that are vulnerable to UHI effects in the region. We found strong evidence for a high level of public awareness about the beneficial ecosystem services that urban trees can provide. A broad spectrum of beneficial tree services were valued highly by the community in their urban environment including the planting of native trees that can attract and provide food for preferred wildlife; provide shade and reduce heat; allow for a strong connection with nature; have the potential to store carbon to mitigate climate change; provide a level of protection from bushfires; have aesthetically pleasing properties; and produce food for people. At the same time, however, community concerns about tree disservices were concentrated primarily on root damage to infrastructure as well as property damage and injury from falling branches. Our elicitation of community attitudes to tree services and disservices will allow for residents’ most important values and strongest concerns about trees to be explicitly taken into account when establishing a community-inclusive approach to urban tree planting. 

Community perceptions of ecosystem services and disservices linked to urban tree plantings

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